Such a tappet clearance compensation device proceeds from the generic DE 199 42 983 A1. This is here designed as a hydraulic support element for a rocker lever of a valve gear of an internal combustion engine. For the purposes of tappet clearance compensation its pressure piston is slightly moveable in an axial direction relative to the housing. If the internal combustion engine is switched off whilst the cam acting on the cam follower is lifting, the pressure piston subsides onto the facing end face of the housing.
Unwanted air bubbles can accumulate in the high pressure chamber of the aforementioned tappet clearance compensation device. This occurs even before the internal combustion engine is started up and during operation of the engine. The air bubbles in the high pressure chamber lead to an unwanted compressibility of the tappet clearance compensation device, with the disadvantages sufficiently familiar to the person skilled in the art. Any escape of the air bubbles would at best be accomplished via the leakage gap between the internal element and the housing, which is unsatisfactory, however, since this process takes too much time. It is also possible, for example, that the air bubbles will accumulate precisely in an annular space between the outer shell of the submerged internal element and the base-side annular enlargement of the housing.
In the high pressure chamber unwanted particles can moreover accumulate, as need not be further explained to the person skilled in the art. These exist, for example, due to original contamination during the production process, or to particles such as abrasion entrained by the hydraulic fluid. These particles adhere to the outer shell of the pressure piston and can get into the leakage gap in the next tappet clearance compensation sequence, in which the pressure piston performs an axial movement out of the housing bore. This can lead to a jamming of the pressure piston in the bore of the housing, with the result that a tappet clearance compensation function of the tappet clearance compensation device fails or the valve lift can no longer be performed correctly. The tendency of unwanted particles to accumulate is further encouraged in that on the outer shell of the sunken pressure piston there is relatively little space available in a radial direction towards the annular enlargement (recess).
Attempts have been made to solve the problem of original contamination outlined above through costly flushing measures. Preventing unwanted particles from getting into the high pressure chamber by means of separators such as strainers, magnets etc. installed directly upstream of the actual tappet clearance compensation device is also known.